Stainless steel wire products and method of making the same



United States Patent 3,395,528 STAINLESS STEEL WIRE PRODUCTS AND METHODOF MAKING THE SAME Wilbert A. Lucht, Orange, -Conn., assignor to UnitedStates Steel Corporation, a corporation of Delaware No Drawing. FiledFeb. 11, 1966, Ser. No. 533,116 6 Claims. (Cl. 57-145) ABSTRACT OF THEDISCLOSURE A method of making stainless steel wire in which a hot rolledrod of astenitic stainless steel having a specific composition is colddrawn to reduce its area between 30 and 75% after which it is stressrelieved at a temperature between 850 and 1200 F. A second cold drawingstep reduces its cross sectional area at least 40% with the totalreduction being at least 85% of the cross sectional area of the hotrolled rod. The product may then be stress relieved at a temperaturebetween 850 and 1200 F. The stainless steel wire so produced has aminimum tensile strength of 300,000 lbs. per sq. in. and is capable ofwithstanding at least 25 twists in a length of wire 100 times itsdiameter.

This invention relates to stainless steel wire products and to a methodof making the same, and particularly relates to austenitic stainlesssteels containing 17 to 20% chromium, 7 to 10% nickel, and .03 to .70%carbon. Stainless Steel Types 302 and 304 are in this category. Suchsteels are made into wire which in many cases is used to make wire rope.Wire of this type, produced in the normal manner is very poor intorsion. Wire rope should also have high tensile strength and goodductility, which properties are not particularly good when the steels ofthe above type are processed in the usual manner.

Therefore it is an object of my invention to provide a method of makingstainless steel wire which has better ductility, higher torsionalproperties and higher tensile strength than normally processed wire.

Another object is to provide a method of making a stainless steel wirerope with wire having high torsional properties and high tensilestrength.

A still further object is to provide a stainless steel wire producthaving good ductility, high torsional properties and high tensilestrength.

These and other objects will be more apparent after referring to thefollowing specification.

According to my invention, I start with an elongated austeniticstainless steel member having the composition disclosed above and whichhas been processed in the usual manner. This member may be a hot rolledrod which has been cooled after hot rolling in such a manner that it isessentially in an annealed state, or it may be processed wire which hasbeen annealed in the usual manner. I first subject this member to a colddrawing step in which its cross-sectional area is reduced between 30 and75%. I find it necessary to have a minimum reduction of 30% in orderthat the product will not be too brittle for the further drawingoperation discussed below. On the other hand, if the reduction is above75%, costs will increase due to drawing difiiculties and heat treatingwithout obtaining any further improvement. The drawn member is thenstress relieved at a temperature between 850 and 1200 F. Subsequently,it is subjected to a second cold drawing step in which itscrosssectional area is reduced at least 40%. The total reduction in thetwo drawing steps must be at least 85 of the cross sectional area of thestarting member.

When using my improved wire in the manufacture of wire rope, I find itdesirable to make the wire rope in 'ice the usual manner and then tostress relieve it at a temperature of between 850 and 1200 F. For someother uses of the wire it is also desirable to stress relieve the wirein this manner after the second reduction.

One particular rope has been made as follows:

A Type 304 annealed wire of .135" diameter was given a reduction to.068" and was then stress relieved for 6 hours at 925 F. This wire wasthen given a 75% reduction to a diameter of .034" so that there was anoverall reduction in area of approximately 93.7%. The wire so producedhad a tensile strength of 344,000 pounds per square inch and 76 twistsin 8". This Wire was then' processed in the usual manner to make aRegular Lay 6 x 36 wire rope with an independent wire rope core, and thewire rope so formed was then stress relieved by heating it to atemperature of 1000 F. This wire rope had a breaking strength of 67,000pounds. A similar wire rope, without the final stress relieving step,had a breaking strength of 55,000 pounds. This compares with a breakingstrength of 44,000 pounds for a similar rope processed in a conventionalmanner.

The wire produced above, when given a final stress relief at 1000 F.,had a tensile strength of 358,000 p.s.i. and 93 twists in 8". A wire ofthe same size and composition produced in a conventional manner had atensile strength of 290,000 pounds per square inch and between 14 and 40turns in 8".

I have found that wire reduced by drawing according to my invention willhave a minimum tensile strength of 300,000 pounds per square inch andcan be given a minimum of 25 twists in a length of wire times the wirediameter, before breaking. The tensile strength will increase as theamount of total reduction increases. In all cases the torsion propertieswill be at least as good as the minimum stated above. Other examples ofType 304 stainless wires made according to my invention, without a finalstress relieving are as follows:

While one embodiment of my invention has been shown and described itwill be apparent that other adaptations and modifications may be madewithout departing from the scope of the following claims.

I claim:

1. The method of making stainless steel wire having high torsionalproperties, good ductility and high tensile strength which comprisesproviding an elongated austenitic stainless steel member containing 17to 20% chromium, 7 to 10% nickel and .03 to .70% carbon, cold drawingsaid member to reduce its cross sectional area between 30 and 75%, thenstress relieving said drawn member at a temperature of between 850 and1200 F., then cold drawing said member to reduce its cross sectionalarea at least 40% with the total reduction being at least 85% of thecross sectional area of the starting member.

2. The method of making stainless steel wire accord ing to claim 1including the step of stress relieving the member after the seconddrawing at a temperature between 859 and 1200 F.

3. The method of claim 1 including the step of stranding wires togetherafter the second drawing step to produce a wire rope.

4. The method of claim 3 including the step of stress relieving the wirerope at a temperature between 850 and 1200 F.

3 4 5. Stainless steel Wire containing 17 to 20% chromium, 3,035,4035/1962 Grimes et al. 57l45 7 to 10% nickel and .03 to .70% carbon, saidwire 3,070,871 1/1963 Ryckebosch. having a minimum tensile strength of300,000 lbs. per 3,217,833 11/1965 Peterson 6t 57-466 XR sq. in. andcapable of withstanding at least 25 twists in OTHER REFERENCES 21 lengthof Wire 100 times the wire diameter.

6. A fatigue resistant wire rope made of stainless steel Publication:Edwards How Edwards Wire Rope Is Made, published June 1955. Original ingroup wires of claim 5.

References Cited 366 class; 57/145 UNITED STATES PATENT FRANK J. COHEN,Primary Examiner. 2.40 6 /194 Kr n 7 R w. H. SCHROEDER, AssistantExaminer.

2,767,836 10/1956 Nachtmann 72286 XR

